U.S. President Donald Trump continued to attack the federal judge who blocked a travel ban on citizens of seven mainly Muslim nations on Sunday, as the first major legal battle of the Trump administration intensified.

"Cannot believe a judge would put our country in such peril. If something happens, blame him and court system," Trump tweeted on Sunday. He went on to tweet: "I have instructed homeland security to check people coming into our country very carefully. The courts are making the job very difficult!"

Earlier on Sunday Vice President Mike Pence defended President Trump's attack on Judge James L. Robart of Sunday for blocking his executive order Friday.

Just cannot believe a judge would put our country in such peril. If something happens blame him and court system. People pouring in. Bad!

Trump blasted Judge James Robart as a "so-called judge" on Saturday, a day after the Seattle jurist issued a temporary restraining order on the ban. A U.S. appeals court later on Saturday denied the government's request for an immediate stay of the ruling.

"The president of the United States has every right to criticize the other two branches of government," Pence said on the NBC program "Meet the Press."

It is unusual for a sitting president to attack a member of the judiciary, which the U.S. Constitution designates as a check on the power of the executive branch and Congress.

The judge opens up our country to potential terrorists and others that do not have our best interests at heart. Bad people are very happy!

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"I think it is best not to single out judges for criticism," Senate Majority Leader Mitch McConnell said on CNN's "State of the Union" program. "We all get disappointed from time to time at the outcome in courts on things that we care about. But I think it is best to avoid criticizing judges individually."

Republican Senator Ben Sasse, a vocal critic of Trump, was less restrained.

"We don't have so-called judges ... we don't have so-called presidents, we have people from three different branches of government who take an oath to uphold and defend the Constitution," he said on ABC News program "This Week."

The ruling by Robart, appointed by former Republican President George W. Bush, along with the decision by the 9th U.S. Circuit Court of Appeals in San Francisco to deny the government's request for an immediate stay dealt a blow to Trump barely two weeks into his presidency.

It could also be the precursor to months of legal challenges to Trump's push to clamp down on immigration, including through the construction of a wall on the U.S.-Mexican border.

The businessman-turned-politician, who during his presidential campaign called for a temporary ban on Muslims entering the United States, has vowed to reinstate the travel ban on citizens from Iran, Iraq, Libya, Somalia, Sudan, Syria and Yemen and a 120-day bar on all refugees.

He says the measures are needed to protect the United States from Islamist militants. Critics say they are unjustified and discriminatory.

Legal uncertainty

The legal limbo will prevail at least until the 9th Circuit Court of Appeals rules on the government's application for a stay of Robart's ruling. The court is now awaiting further submissions from the states of Washington and Minnesota on Sunday, and from the government on Monday. The final filing is due at 1700 PST on Monday (0100 GMT on Tuesday).

The uncertainty has created what may be a short-lived opportunity for travelers from the seven affected countries to get into the United States.

"This is the first time I try to travel to America. We were booked to travel next week but decided to bring it forward after we heard," said a Yemeni woman, recently married to a U.S. citizen, who boarded a plane from Cairo to Turkey on Sunday to connect with a U.S.-bound flight. She declined to be named for fear it could complicate her entry to the United States.

Reacting to the latest court ruling, Iraqi government spokesman Saad al-Hadithi said: "It is a move in the right direction to solve the problems that it caused."

Trump's Jan. 27 travel restrictions have drawn protests in the United States, provoked criticism from U.S. allies and created chaos for thousands of people who have, in some cases, spent years seeking asylum.

In his ruling on Friday, Robart questioned the use of the Sept. 11, 2001 attacks on the United States as a justification for the ban, saying no attacks had been carried out on U.S. soil by individuals from the seven affected countries since then.

For Trump's order to be constitutional, Robart said, it had to be "based in fact, as opposed to fiction".

The 9/11 attacks were carried out by hijackers from Saudi Arabia, the United Arab Emirates, Egypt and Lebanon, whose nationals were not affected by the order.

In a series of tweets on Saturday, Trump attacked "the opinion of this so-called judge" as ridiculous.

"What is our country coming to when a judge can halt a Homeland Security travel ban and anyone, even with bad intentions, can come into U.S.?" he asked.

Trump told reporters at his private Mar-a-Lago resort in Florida late on Saturday: "We'll win. For the safety of the country we'll win."

The Justice Department appeal criticized Robart's legal reasoning, saying it violated the separation of powers and stepped on the president's authority as commander-in-chief.

The appeal said the state of Washington lacked standing to challenge the order and denied that the order "favors Christians at the expense of Muslims."

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